You will have to give me more details on what you mean by "oxygenated" conditions.
You can run the test on how long chlorine dioxide lasts in the mouth by simply mixing up a dose, taking a mouthful, swishing for 10 seconds, then spit it out in a clean glass. Check it for chlorine dioxide.
The mouth, throat, stomach, and lower GI tract are all protected by mucous. Mucous is a type of biofilm.